1. Field of the Invention
The present invention relates to a voltage monitoring system of electric power source for floppy disk drive circuit and more particularly to a voltage monitoring system for battery driven small size floppy disk drive circuit.
2. Description of the Prior Art
There are known various information recording media used as external memories for computers. Among them, magnetic disks are currently utilized since they are randomly accessible and easily handled. Recently, a so-called floppy disk has been developed which includes a substrate of flexible plastic sheet having one or two faces coated with magnetically storing layers. The floppy disk is increasingly used over the broad range of applications since it has many advantages, for example, in that the floppy disk is cheaper than hard disks and in that the floppy disk can easily be changed to another floppy disk to increase the capacity of memory.
More recently, a so-called cartridge type micro-floppy disk has been developed in which a floppy disk as an information recording medium is contained within a cartridge of hard plastic casing or the like. This is advantageous in that the floppy disk can extremely easily and simply be carried and handled while preventing the recording face(s) thereof from being damaged and contaminated by any foreign matters. Such a micro-floppy disk cartridge is broadly being utilized as an excellent external memory in small-size computers and particularly personal and domestic computers.
In the micro-floppy disk cartridge, the micro-floppy disk is housed within a hard plastic casing which has a shutter mechanism for preventing the READ/WRITE faces of the disk from being exposed to protect the recording faces substantially completely from any foreign matters. Thus, a user can handle the floppy disk without his additional attention to the damage and contamination of the recording faces in the floppy disk. The micro-floppy disk cartridge also is mailable.
In order to most utilize the advantages of the micro-floppy disk cartridge, a floppy disk drive therefor must have various new performances different from those of the conventional 8-inch floppy disk drive. Main requirements to the micro-floppy disk drive is that it can be reduced in size and can be operated with the minimum power consumption.
Computers themselves are remarkably being reduced in size while increasing their processing speed and capacity. It is thus known that the entire size of a computer system depends on the dimension and arrangement of a keyboard, monitor and external memory. Consequently, the micro-floppy disk drive should necessarily be reduced in size and operated with the minimum power consumption such that a portable micro-computer can be realized.
In the above floppy disk drive with a minimum power consumption, monitoring of electric power source is required to maintain a stable read/write operation of the floppy disk drive.
In the monitoring system in the prior art prepared therein was single detector which detects one predetermined minimum standard level of voltage for each electric power supply system. In power supply circuits supplying 5 V (Volts) and 12 V for activating a floppy disk drive, for example, the minimum standard voltage from 3.4 V to 3.8 V was picked up for the detecting level in the 5 V power supply system, and the second minimum standard voltage from 10.5 V to 11 V was picked up for the detecting level for the 12 V power supply system. One detecting level was established in each of the 5 V and 12 V power supply systems.
In the floppy disk drive circuit in the prior art, electric power was supplied from a stabilized power supply with the guaranteed accuracy of .+-.5%. The voltage supplied from such power supply was kept stabilized in the normal state. Even if abnormal state occurred in the prior art, the voltage drop mode was established in such that the voltage suddenly dropped to 0 or to the extremely lower voltage. Accordingly, monitoring level of the voltage in the electric power supply was sufficient to establish at one level with which the disk driving operation can be guaranteed, and the circuit operation can be protected in an abnormal state that the voltage was detected to be lower than such level.
However, considering that the floppy disk is getting popular among portable gears as is seen nowadays, it is indispensable to use batteries for the electric power source. The battery gradually drops its power comparatively in a short while. Therefore, one level monitoring method of the voltage in the electric power source will cause the problem in establishment of such level when we are going to use the battery as long as possible.
Specifically, as the power source voltage drops down in the floppy disk drive, the write operation becomes inaccurate at the beginning. Further drop of the voltage makes the read (reproducing) operation and/or the motor drive becomes unstable. When the level is established at the single voltage which guarantees the firm write operation, the voltage lower than this level determines to be out of the useable range by means of one level monitoring method, and the battery can be only used for an extremely short period, which causes in frequent exchange of batteries.
On the contrary, when the detecting level is established at as low value as guarantees the read (reproducing) operation, and the operations of a circuit driving a stepping motor to feed a head and a logic circuit in order to expand the useable period of battery voltage, there will be such problems for memory devices that the inaccurate write operation makes incorrect recording and that the correct data already written in are possibly destroyed, since there exists non-protection area therein for the write operation.